1. Field of the Invention
The present invention relates to a lamp protection apparatus and an operation method thereof, and more particularly to a series lamp duplexing protection apparatus and an operation method thereof.
2. Description of Related Art
Fluorescent Lamp (FL) has been applied to the backlight system of LCD because of its advantages of better emission efficiency and longer life time compared to traditional lamp. With advancement of the LCD technology, it is possible to manufacture LCD with larger screen size than before. By this trend, a multiple-lamp system applied to LCD has also become more sophisticated.
In the multiple-lamp system, usually multiple controllers of cold cathode fluorescent lamps are used. Due to the structure of the multiple controllers, the communication between these controllers is more complicated than that of a single controller. The improvement of communication between the controllers becomes important, especially when the improvement is essentially related to safety concern. Traditional protection approach usually adopts a parallel protection system. Each of lamps coupled to the common control line in order to obtain protection therefrom. The whole backlight system of LCD is, therefore, protected by such design.
FIG. 5 is a circuit block diagram of a conventional two-lamp protection apparatus. Referring to FIG. 5, the two-lamp protection apparatus comprises a first converter 502, a second converter 522, a first fluorescent lamp 504, a second fluorescent lamp 524, a first lamp current detecting circuit 506, a second lamp current detecting circuit 526, a first lamp current decision circuit 508, a second lamp current decision circuit 528, a first lamp current control circuit 514, a second lamp current control circuit 534 and an AND gate 540. The first lamp current control circuit 510 comprises a first feedback compensation circuit 512 and a first pulse width modulator (PWM) 514. The second lamp current control circuit 530 comprises a second feedback compensation circuit 532 and a second pulse width modulator (PWM) 534. The circuits constitute the current modification circuit for stabilizing the operational current and output brightness of the first fluorescent lamp 504 and the second fluorescent lamp 524.
For protection design of the prior art technology, the detection of the operational currents of the first fluorescent lamp 504 and the second fluorescent lamp 524 are used to determine whether the fluorescent lamp fails. The first lamp current decision circuit 508 and the second lamp current decision circuit 528 output a first lamp turn-off signal and a second lamp turn-off signal, respectively, to the AND gate 540. According to these turn-off signals, the AND gate 540 outputs signals to the first lamp current control circuit 510 and the second lamp current control circuit 540. When either fluorescent lamp fails, the system controls the first lamp current decision circuit 508 or the second lamp current decision circuit 528 to remove the power supplied to the first fluorescent lamp 504 or the second fluorescent lamp 524.
FIG. 6 is a circuit block diagram of a conventional three-lamp protection apparatus. In addition to these circuits described in FIG. 5, the three-lamp protection apparatus in FIG. 6 also comprises a third converter 642, a third fluorescent lamp 644, a third lamp current detecting circuit 646, a third lamp current decision circuit, a third lamp current control circuit 650 and AND gates 662 and 664. The third lamp current control circuit 650 comprises a third feedback compensation circuit 652 and a third PWM 654. The operations of the three-lamp protection apparatus in FIG. 6 are similar to those of the two-lamp protection apparatus in FIG. 5. Detailed descriptions are not repeated.
According to the above description with reference to FIGS. 5 and 6, an additional lamp circuit must include an AND gate. Each decision circuit must be separately coupled to the AND gate and the output terminal of one of the AND gates must be coupled to the control circuits. As a result, the number of devices in the circuit is increased and the circuit is complicated. When more and more lamps are used, manufacturing costs and the complexity of the circuit are unfavorably increased due to the increase of devices.